1. Field of the Invention
The present invention relates to an actuating plunger of an electromagnetic pump, and more particularly to an actuating plunger which can be easily manufactured, and by which the operational efficiency of the electromagnetic pump can be improved and the operational. noise thereof can be reduced.
2. Prior Arts
An electromagnetic pump is an appliance for supplying fluid, and is generally used for supplying oil to a burner in a boiler system.
An electromagnetic pump has an actuating plunger alternating up and down in a hollow cylinder by an electromagnetic force so as to pressurize the oil.
FIG. 4 shows a conventional actuating plunger 250 as described above. Conventional actuating plunger 250 has a plunger head 251 and a piston 252.
FIGS. 5A and 5B are respectively a side sectional view and a plan view of plunger head 251. As shown, plunger head 251 has a cylindrical wall 253, and a bottom portion 254 formed integrally with the lower circular end of cylindrical wall 253.
Bottom portion 254 has a center hole 255, and four connecting holes 256 disposed around center hole 255 which are spaced apart from each other at regular circumferential intervals. Piston 252 is fixed in center hole 255. The space above and the space below plunger head 251 are interconnected to each other through connecting holes 256.
Actuating plunger 250 having the above construction moves up and down at a high speed by means of the electromagnetic force intermittently applied to a magnetic core by a solenoid, the magnetic core being disposed above the actuating plunger, so that the oil passing through the space under piston 252 is pressurized.
While actuating plunger 250 is moving up and down at a high speed, the oil in the space above piston 252 flows between the space above and the space below plunger head 251 through connecting holes 256. In this case, the oil provides a damping force for an up-and-down movement of actuating plunger 250. That is, the up-and-down movement of actuating plunger 250 is hindered by a viscous friction of the oil passing through connecting holes 256.
The larger the sectional area of the oil path or connecting holes 256 becomes, the less the damping force hindering the up-and-down movement of actuating plunger 250 becomes. The up-and-down movement of actuating plunger 250 is hindered relatively largely because the sectional area of connecting holes 256 is relatively small.
Meanwhile, when the conventional actuating plunger 250 of the electromagnetic pump as described above is manufactured, center hole 255 is first formed by cutting through the center of the bottom portion 254. as shown in FIG. 5A, and then four connecting holes 256 are formed around center hole 255 by the same cutting process in such a manner that four connecting holes 256 are spaced apart from each other at regular circumferential intervals. Then, piston 252 is inserted and fitted in center hole 255 so that the manufacturing process of actuating plunger 250 is completed.
Chips are produced during the cutting process of center hole 255 and connecting holes 256, and are not completely removed out of these holes while actuating plunger 250 is manufactured but remain in center hole 255 and connecting holes 256. The remaining chips may move together with oil so as to block the exhaust nozzle or to generate noise in operation of the electromagnetic pump.
Further, actuating plunger 250 may vibrate and generate noise during its movement, because a moment may be applied to plunger head 251 in the high-speed alternating movement of actuating plunger 250, when the center of gravity of plunger head 251 and the center of center hole 255 do not coincide with each other.
To prevent such vibration and noise, center hole 255 and connecting holes 256 should be formed in such a manner that the central axis of plunger head 251 and piston 252 is positioned at the centroid of a section of plunger head 251. That is, center hole 255 and connecting holes 256 should be complete circles, respectively and connecting holes 256 should be disposed along a circumference of a phantom circle concentric with center hole 255 and spaced apart from each other at regular circumferential intervals.
However, it is very difficult to cut through plunger head 251 to make center hole 255 and connecting holes 256 in order for the center of gravity of plunger head 251 and the center of center hole 255 to coincide with each other as described above.
Moreover, actuating plunger 250 must have a good magnetic characteristic of ensuring smooth up-and-down movement of actuating plunger 250 by means of the solenoid, and thereby actuating plunger should preferably be made from ferrite iron having a good magnetic characteristic. However, it is difficult to cut the ferrite iron, and the systematic structure of the ferrite iron can be changed and its magnetic characteristic can deteriorate due to heat generated during its cutting process and to cooling conditions after the cutting.
Therefore, generally the conventional actuating plunger 250 of an electromagnetic pump has been made from an alloy comprised of iron (Fe), silicon (Si), manganese (Mn), carbon (C), phosphorus (P), sulfur (S), and lead (Pb) instead of the ferrite iron. The alloy has inferior magnetic characteristic but superior cutting characteristic and resistance-to-heat compared to the ferrite iron.
As described above, conventional actuating plunger 250 has disadvantages that chips are produced in its cutting process, that the removal of the chips is very difficult, and that the chips can block the exhaust nozzle or generate noise. Moreover, the conventional actuating plunger can not be made from ferrite iron having good magnetic characteristic due to the restriction in relation to its cutting. The conventional actuating plunger exhibits low efficiency in utilizing energy because its up-and-down movement is hindered relatively largely by a viscous resistance of oil. In addition, it is difficult to cut through plunger head 251 to make center hole 255 and connecting holes 256 in such a manner to prevent a moment from being applied to plunger head 251 in its operation.